Misaponin B Induces G2/M Arrest, Cytokinesis Failure and Impairs Autophagy

Saponins are a group of naturally occurring plant glycosides with the features of their strong foam-forming properties and multibiological effects such as antitumor activity. Though Misaponin B, one of the triterpenoid saponins from Madhuca longifolia, is known to have spermicidal and antioxidant activity, the other biological activities have been never reported so far. Thus, in the present study, the antitumor mechanism of Misaponin B was investigated in A549 and AsPC-1 cancer cells. Misaponin B exerted significant cytotoxicity in A549, H460, SKOV3, and AsPC-1 cancer cells. Among them, A549 and AsPC-1 cells were more susceptible to Misaponin B. Misaponin B induced G2/M arrest and cytokinesis failure and increased the expression of LC3B and p62 with autophagic vacuoles and GFP-LC3 punctae in A549 and AsPC-1 cells. Furthermore, Misaponin B suppressed autophagy flux in A549 cells transfected by GFP-mRFP-LC3 constructs by showing merged yellow color by autophagy flux assay. Overall, our findings provide evidences that Misaponin B induces G2M arrest and impairs autophagy in A549 and AsPC-1 cells.

Foam Generation in Flow Across a Sharp Permeability Transition: Effect of Velocity and Fractional Flow

Summary Foam reduces gas mobility and can help improve sweep efficiency in an enhanced-oil-recovery (EOR) process. For the latter, long-distance foam propagation is crucial. In porous media, strong foam generation requires that the local pressure gradient exceed a critical value (▿Pmin). Normally, this happens only in the near-well region. Away from wells, these requirements might not be met, and foam propagation is uncertain. It has been shown theoretically that foam can be generated, independent of pressure gradient, during flow across an abrupt increase in permeability (Rossen 1999). The objective of this study is to validate theoretical explanations through experimental evidence and to quantify the effect of fractional flow on this process. This article is an extension of a recent study (Shah et al. 2018) investigating the effect of permeability contrast on this process. In this study, the effects of fractional flow and total superficial velocity are described. Coreflood experiments were performed in a cylindrical sintered-glass porous medium with two homogeneous layers and a sharp permeability jump in between, representing a lamination or cross lamination. Unlike previous studies of this foam-generation mechanism, in this study, gas and surfactant solution were coinjected at field-like velocities into a medium that was first flooded to steady state with gas/brine coinjection. The pressure gradient is measured across several sections of the core. X-ray computed tomography (CT) is used to generate dynamic phase-saturation maps as foam generates and propagates through the core. We investigate the effects of velocity and injected-gas fractional flow on foam generation and mobilization by systematically changing these variables through multiple experiments. The core is thoroughly cleaned after each experiment to remove any trapped gas and to ensure no hysteresis. Local pressure measurements and CT-based saturation maps confirm that foam is generated at the permeability transition, and it then propagates downstream to the outlet of the core. A significant reduction in gas mobility is observed, even at low superficial velocities. Foam was generated in all cases, at all the injected conditions tested; however, at the lowest velocity tested, strong foam did not propagate all the way to the outlet of the core. Although foam generation was triggered across the permeability boundary at this velocity, it appeared that, for our system, the limit of foam propagation, in terms of a minimum-driving-force requirement, was reached at this low rate. CT images were used to quantify the accumulation of liquid near the permeability jump, causing local capillary pressure to fall below the critical capillary pressure required for snap-off. This leads to foam generation by snap-off. At the tested fractional flows, no clear trend was observed between foam strength and fg. For a given permeability contrast, foam generation was observed at higher gas fractions than predicted by previous work (Rossen 1999). Significant fluctuations in pressure gradient accompanied the process of foam generation, indicating a degree of intermittency in the generation rate—probably reflecting cycles of foam generation, dryout, imbibition, and then generation. The intermittency of foam generation was found to increase with decreasing injection velocities and increasing fractional flow. Within the range of conditions tested, the onset of foam generation (identified by the rise in ▿P and Sg) occurs after roughly the same amount of surfactant injection, independent of fractional flow or injection rate.

Dimensionality-Dependent Foam Rheological Properties: How To Go From Linear to Radial Geometry for Foam Modeling and Simulation

Summary Numerous laboratory and field tests reveal that foam can effectively control gas mobility and improve sweep efficiency, if correctly designed. It is believed that there is a significant gap between small laboratory-scale experiments and large field-scale tests because of two main reasons: (1) Typical laboratory flow tests are conducted in linear systems, whereas field-scale foam enhanced-oil-recovery (EOR) processes are performed in radial (or spherical partly) systems and (2) through the complicated in-situ lamella creation/coalescence mechanisms and non-Newtonian behavior, foam rheology depends on the geometry and dimensionality. As a result, it is still an open question as to how to translate laboratory-measured data to field-scale treatments. Motivated by earlier studies of Kovscek et al. (1994, 1997), this study investigates how such dimensionality-dependent foam rheological properties are affected by different injection conditions on small and large scales, with a mechanistic foam-modeling technique. Complex foam-flow characteristics such as three foam states (weak-foam, strong-foam, and intermediate states) and two steady-state strong-foam regimes (high-quality regime and low-quality regime) lie in the heart of this analysis. The calculation results from small radial and spherical systems showed that (1) for strong foams in the low-quality regime injected, foam mobility decreased [or mobility reduction factor (MRF) increased] significantly with distance showing a good sweep efficiency; (2) for strong foams in the high-quality regime, the situation became more complicated—near the well, foam mobility decreased, but away from the well, foam mobility increased with distance, which eventually gave a relatively low sweep efficiency; and (3) for weak foams injected, foam mobility increased with distance showing a poor sweep efficiency. The results implied that the use of a fixed value of MRF, which is a common practice in field-scale reservoir simulations, might lead to a significant error. When the method was applied to a larger scale, it was shown that strong foams could propagate deeper into the reservoir at higher injection rate, higher injection pressure, and at lower injection foam quality. Foam-propagation distance was very sensitive to these injection conditions for strong foams in the high-quality regime, but much less sensitive for strong foams in the low-quality regime.

Gas-Injection Rate Needed for SAG Foam Processes To Overcome Gravity Override

Summary Gravity override is a severe problem in gas-injection enhanced-oil-recovery (EOR) processes, especially in relatively homogeneous formations. Foam can reduce gravity override. Shan and Rossen (2004) show that the best foam process for overcoming gravity override is one of injecting a large slug of surfactant followed by a large slug of gas, injected at constant, maximum-allowable injection pressure. This process works because foam collapses near the injection well, giving good injectivity simultaneously with mobility control at the leading edge of the gas bank. The supply of gas that would be needed to maintain constant injection pressure is a concern for EOR processes in which gas is produced industrially or from a separations plant with limited capacity: The available gas stream may not be sufficient for the optimal process. We show that for such a process, the pressure drop across the foam bank back to the injection well, at fixed injection rate, is nearly constant as the foam bank propagates radially outward. From this result, one can derive a simple formula to predict the rate of gas injection required for each of two limiting cases: An extremely strong foam at the foam front, many times more viscous than the fluids it displaces. In this case, the rate of gas injection required to maintain constant injection pressure is nearly constant, but injection rate is low. A foam just strong enough to maintain mobility control at its leading edge. In this case, injection rate required to maintain constant injection pressure increases steeply with time. Use of the formulae provides a quick initial estimate of how gas-injection rate must vary over the duration of the EOR process to maintain an optimal process. The fit to simulations of surfactant-alternating-gas (SAG) foam-injection rate in a five-spot pattern is remarkably good, especially for strong foam, given the simplicity of the model. In addition, we illustrate how one would determine the properties of a foam that would fit the available gas stream. This criterion then could guide the development of a surfactant formulation with these properties.

Multiple Foam States and Long-Distance Foam Propagation in Porous Media

Summary Creation of low-mobility foam for enhanced oil recovery (EOR) is triggered by an increase in superficial velocity; thereafter, injection rate can be reduced to lower values, and strong foam remains at velocities at which weak foam was previously observed. Here, we consider whether strong foam created near an injection well can propagate to large distances from the well where superficial velocity is much smaller. We study strong-foam propagation with finite-difference simulations and Riemann solutions, applying a population-balance foam model that represents the multiple steady states of foam. Our simulations show that strong foam cannot displace directly the initial high-water-saturation bank initially in the reservoir at low superficial velocities; it pushes a weak-foam state with lower velocity that in turn displaces the bank ahead. Our traveling-wave solutions show that strong foam propagates more slowly as superficial velocity decreases and stops propagating at yet lower superficial velocities, in agreement with the experiment. Failure of propagation occurs at superficial velocities greater than that at which the strong-foam state disappears; it raises concerns for long-distance propagation of strong foam created near the injection well. In the context of the model, it is not extraordinary destruction of foam at the front that slows the propagation of strong foam, but failure of foam (re-)generation at the front. Our model also represents for the first time a process where strong foam is created near the exit of a core and then propagates upstream, as seen in some experiments.

Dynamic Simulations With an Improved Model for Foam Generation

Summary We present the first 1D simulations of dynamic foam displacements with a population-balance model incorporating bubble creation controlled by pressure gradient. For the first time, a population-balance model is fit to steady-state experimental data for both the three foam states (coarse foam, intermediate, and strong foam) and the two strong-foam regimes (low-quality and high-quality) observed in laboratory studies. Simulations confirm the stability of the coarse-foam and strong-foam states to small perturbations, and the instability of the intermediate state, at fixed injection rates. In dynamic displacements, the model shows foam generation as injection rates increase, or as liquid fraction of injected fluids increases, in agreement with laboratory observations. When coarse foam is created instead of strong foam, there is a narrow region of finer foam predicted near the gas displacement front. This region appears to play a role in foam generation. However, in the limited cases examined here, foam generation occurs at roughly the same injection rate as predicted by local-steady-state theory. Because of this narrow region of finer-textured foam, fronts can be sharper than estimated from fractional-flow theory assuming a constant effective gas viscosity at its steady-state value behind the displacement front. If a strong foam forms in the low-quality regime, the kinetics of foam generation and destruction affects the length of the entrance region in which foam forms. Therefore, the length of the entrance region can be used to calibrate the kinetic parameters in the model. The displacement front and the bank behind it, however, are essentially what one would have predicted from local-steady-state modeling. The complexities of population-balance modeling are not necessary, if it is known that strong foam will be created. Introduction Foam can improve sweep efficiency in gas-injection improved oil recovery (IOR) processes (Schramm 1994; Rossen 1996; Terdre 2003), redirect acid flow in matrix acid stimulation (Gdanski 1993; Cheng et al. 2002; Nguyen et al. 2003), and increase the efficiency of environmental remediation of aquifers (Hirasaki et al. 2000; Mamun et al. 2002). A continuing goal of foam research is the development of a fully mechanistic, predictive model. This paper describes efforts toward such a model and insights gained from application of the model to dynamic displacements. Before providing a detailed description of the model, it is worthwhile to review the mechanisms of foam in porous media and the experimental observations that the model attempts to reproduce.